This book is intended to help satisfy an urgent requirement for up-to date comprehensive texts at graduate and senior undergraduate levels on the subjects in non-destructive testing (NDT). The subject matter here is confined to electrical and magnetic methods, with emphasis on the widely used eddy current and magnetic flux leakage methods (including particle inspection), but proper attention is paid to other techniques, such as microwave and AC field applications, which are rapidly growing in importance. Theoretical analyses relating to the various methods are discussed and the depths of presentation are often governed by whether or not the information is readily available elsewhere. Thus, for example, a considerable amount of space is devoted to eddy current theory at what the author considers to be a reasonable standard and not, as usually experienced, in either a too elementary manner or at a level appreciated only by a postgraduate theoretical physicist. The inclusion of the introductory chapter is intended to acquaint the reader with some of the philosophy of NDT and to compare, briefly, the relative performances of the more important methods of testing.